Labelling list of points in PGF scatter plot

Question

I have the following input file (sample.txt):

A 1 2
B 23 2
C 2 34
D 12 22
E 23 3
F 34 12

I want to create a scatter plot where the second column is the x-axis, the third column is the y-axis, and the first column is the label for each point.

However, I want to only label points that exist in a list L = [B,D,E]

The list which should be defined in the source code (i.e. not in a file), can be changed and should reflect in the plot.

I'm having a difficult time getting this done in PGF plots. Any ideas?

Here's my attempt so far

\documentclass{standalone}
\usepackage{pgfplots}
\pgfplotsset{compat=1.11}
\begin{document}

\begin{tikzpicture}
\begin{axis}
    \addplot+ [mark = x, 
        only marks,
        visualization depends on={value \thisrowno{0}}
    ] table[x index = 1, y index = 2] {annot_no_align.out};

\end{axis}
\end{tikzpicture}
\end{document}

Note: as you can probably tell, I'm a beginner in PGFPlots.

Answer 1

So this is a combination of node near coords and some if-exercise.

one can find the definition of \pgfutil@in@ in pgfutil-common.tex. Also one can look up LaTeX's \includeonly and BEAMER's \includeonlyframes.

\documentclass{standalone}
\usepackage{pgfplots}
\pgfplotsset{compat=1.11}
\begin{document}

\makeatletter
\def\labelonly{BDF}
\def\labelcheck#1{
    \edef\pgfmarshal{\noexpand\pgfutil@in@{#1}{\labelonly}}
    \pgfmarshal
    \ifpgfutil@in@[#1]\fi
}
\makeatother

\begin{tikzpicture}
\begin{axis}
    \addplot[
        mark=*,
        only marks,
        point meta=explicit symbolic,
        nodes near coords={
            \labelcheck{\pgfplotspointmeta}
        }
    ]
        table[header=false,meta index=0,x index=1,y index=2]{
            A 1 2
            B 23 2
            C 2 34
            D 12 22
            E 23 3
            F 34 12
        };
\end{axis}
\end{tikzpicture}
\makeatletter

\end{document}

Update

Here is a better solution when you prefer CSV. I am using native \pgfkeys features so you probably already know what is dangerous and what is not. (e.g. comma is dangerous.)

\documentclass{standalone}
\usepackage{pgfplots}
\pgfplotsset{compat=1.11}
\begin{document}

\pgfkeys{
    /prepare label/.style={
        /print label/\detokenize{#1}/.code={\ttfamily\detokenize{#1}}
    },
    /prepare label/.list={^_^,@_@,T_T}
}
\begin{tikzpicture}
\begin{axis}
    \addplot[
        mark=*,
        only marks,
        point meta=explicit symbolic,
        nodes near coords={
            \pgfkeys{/print label/\pgfplotspointmeta/.try}
        }
    ]
        table[header=false,meta index=0,x index=1,y index=2]{
            ^_^   1  2
            >_<  23  2
            @_@   2 34
            Q_Q  23  3
            T_T  12 22
            =_=  34 12
        };
\end{axis}
\end{tikzpicture}

\end{document}